我有一个生锈实现如下,在默认实现中,对于枚举,我需要返回最后一个元素,我需要实现它而不需要对其进行硬编码。
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub enum Region<CountryId> {
None,
Category(CountryId),
}
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub struct Litrature1<CountryId> {
pub Seek: Region<CountryId>,
pub Write: Region<CountryId>,
}
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub struct Litrature2<CountryId> {
pub Seek: Region<CountryId>,
pub Write: Region<CountryId>,
pub Work: Region<CountryId>,
}
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub enum Alphabets<CountryId> {
A1(Litrature1<CountryId>),
A2(Litrature1<CountryId>)
}
impl<CountryId> Default for Alphabets<CountryId> {
fn default() -> Self {
// How to return the last element of the enum as default?
Alphabets<CountryId>::A2
}
}
我不确定如何使这项工作
我假设您基本上想要默认值,每个区域默认为Region::None
。在这种情况下,最有意义的是在每个嵌套类型上定义Default
,例如
Region
的默认值
impl<CountryId> Default for Region<CountryId> {
fn default() -> Self {
Region::None
}
}
Litrature1
的默认值
impl<CountryId> Default for Litrature1<CountryId> {
fn default() -> Self {
Litrature1 {
Seek: Default::default(),
Write: Default::default(),
}
}
}
Litrature2
的默认值
impl<CountryId> Default for Litrature2<CountryId> {
fn default() -> Self {
Litrature2 {
Seek: Default::default(),
Write: Default::default(),
Work: Default::default(),
}
}
}
Alphabets
的默认值
impl<CountryId> Default for Alphabets<CountryId> {
fn default() -> Self {
Alphabets::A2(Default::default())
}
}
(Qazxswpoi)